The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time computers have become indispensable in many fields of human endeavor including engineering design, machine and process control, and information storage and access. In the early days of computers, companies such as banks, industry, and the government would purchase a single computer which satisfied their needs, but by the early 1950's many companies had multiple computers and the need to move data from one computer to another became apparent. At this time computer networks began being developed to allow computers to work together.
Computer networks are capable of performing jobs that no single computer could perform and they allow low cost personal computer systems to connect to larger systems to perform tasks that such low cost systems could not perform alone. In order for computer systems to cooperate in a network to perform some complex job, software must be developed which efficiently delegates parts of the chore or tasks to different computers in the network. One of the recent advances in the field of software development has been the emergence of object-oriented programming technology.
The goal of using object-oriented programming is to create small, reusable sections of program code known as objects that can be quickly and easily combined and re-used to create new programs. This is similar to the idea of using the same set of building blocks again and again to create many different structures. The modular and re-usable aspects of objects typically speeds development of new programs, thereby reducing the costs associated with the development cycle. In addition, by creating and re-using a group of well-tested objects, a more stable, uniform, and consistent approach to developing new computer programs can be achieved.
Although object-oriented programming offers significant improvements over other programming types, program development still requires significant amounts of time and effort, especially if no preexisting objects are available as a starting point. Consequently, one approach has been to provide a program developer with a set of pre-defined, interconnected classes that create a set of objects. Such pre-defined classes and libraries are typically called object frameworks. Frameworks essentially provide a prefabricated structure for a working program by defining certain classes, class relationships, and methods that a programmer may easily use by appropriate subclassing to generate a new object-oriented program.
An object in an object-oriented computer program typically has attributes defined by state data that determine how the object will behave. If an object is transient, it is created within a process, and terminates when the process ends. If an object is persistent, however, mechanisms are put in place to allow the object to survive the process that creates it so it can be accessed by other processes. A distributed object system results when an object in one process is allowed to access an object in another process. A distributed object environment, as used herein, means any hardware and software configuration and/or combination that allows an object in a first process to access an object in a second process. Examples of known distributed object systems include: 1) a first process and a second process residing on the same computer; 2) a first process and a second processes residing on different computer workstations in a local area network (LAN); and 3) a first process and a second process residing on computers in geographically remote locations that are interconnected using a wide area network (WAN). As technology progresses, other distributed object systems will, no doubt, be developed, and the present invention expressly encompasses all types of distributed object systems, whether now known or developed in the future.
Objects are typically made persistent by storing their state data in a local data store. In many known computer systems, the process of making an object persistent is known as "externalization". Externalization is the means or protocol used in object-oriented programming for transferring data out of an object. In essence the "state data" that defines the attributes of an object are "externalized", or written out of the object, into a different format that is easily stored in the local data store. When the object is needed again, the externalized state data is internalized into an object, creating an exact copy of the object as it previously existed.
Objects that are located on different computer systems may have different attributes that allow the object to be stored in the local data store. For example, one computer system may store data in a flat file (such as a POSIX file) in a standard directory structure, and objects on this computer system will be configured to store their state data in the appropriate file format. A different computer system may store data in a relational data base (RDB), and objects on this computer system will be configured to store their state data in the RDB format.
Known persistent storage systems limit the types of data that can be stored persistently. For example, a particular persistent storage system may only support RDB or POSIX formats. Consequently, users may have access to data that cannot be stored persistently simply because the persistent storage system in use does not support storing data of that particular format. This problem becomes more acute as more computer systems with different persistent storage systems become interconnected in a distributed object environment.
As the need for persistent storage of wide varieties of data formats grows, the need for better mechanisms for storing persistent data becomes more apparent. Without a mechanism that can be readily customized and extended to provide new persistent storage systems, the computer industry will never fully realize the potential and power of sharing data in distributed object systems.